(CNN) -- Twenty-five years ago, I was a Ph.D. student here in Woods Hole, Massachusetts, studying the fate of fallout in the North Atlantic from nuclear weapons testing, when an explosion and fire at the Chernobyl nuclear plant released large quantities of radioactive materials into the surrounding environment. My colleagues and I immediately joined other scientists tracking these radioactive contaminants, which in my case focused on the Black Sea, the closest ocean to the accident site.

A quarter-century later, I can still measure fallout from Chernobyl in the Black Sea, though fortunately at levels that are safe for swimming, consuming seafood and, if you could remove the salt, even drinking. I never thought I'd see another release anywhere near the magnitude of Chernobyl.

As we now know, the tsunami that hit Japan on March 11 caused immediate, widespread devastation on land and failure of cooling systems at the Fukushima Daiichi nuclear power facility. The resulting partial meltdowns, hydrogen explosions and fires at Fukushima released radioactive contaminants into the air and water. In addition, runoff from the attempts to cool the reactors with seawater and fresh water further contaminated the ocean around Fukushima.

Data released by Japanese scientists show cesium-137 concentrations in the waters immediately adjacent to the reactors at levels more than 1 million times higher than previously existed and 10 to 100 times higher in the waters off Japan than values measured in the Black Sea after Chernobyl. For the oceans, this is the largest accidental release of radiation we have ever seen.

But what do these high values mean for ocean life and human health? What will it mean 25 years from now?

We know the ocean has the ability to mix and dilute even these alarmingly high concentrations of contaminants. Indeed, just 15 miles offshore the levels of some contaminants, including cesium-137, with its relatively long 30-year half-life, are already 100 to 1,000 times lower than waters near the reactors, and thus pose little direct hazard for human exposure. We also know that over the short-term, isotopes such as iodine-131, which has an eight-day half-life and has been found in milk and spinach, will decay to insignificant levels.

But there is still too much that we don't know. We still have not measured the full complement of radionuclides released to the oceans, including the highly toxic plutonium. We have not mapped where contaminants are going and how fast they are spreading, so we can't confirm how well our models are predicting dispersion and dilution of these substances.

The groundwater around Fukushima and sediments in the seafloor nearby will likely remain contaminated for decades to come, yet no radionuclide data exist from these sources. There are also large gaps in our knowledge of how marine life assimilates radioactive contaminants, how the process may vary depending on different life stages, or how contaminants will transfer up the food chain to fish and other marine animals. This information will be essential for short-term assessments of threats to transportation, health, fisheries and ocean ecosystems, and for informing nuclear industry regulatory policies and oceanography for decades to come.

Early observations are key to understanding what has occurred. The Japanese have begun ocean field work to fill in some of these gaps in our knowledge, but this is a bigger job than any single country, agency or lab can take on.

If we are to fully grasp the extent of those effects and help mitigate them, the international community must support efforts to immediately undertake comprehensive field studies in the Pacific Ocean near Japan. Follow-up work will be needed for years and decades to come before we are able to say with any certainty that we understand the fate of these radionuclides in the ocean and the effect they have had on the marine environment.

After 25 years, we are just beginning to grasp Chernobyl's legacy. Now Fukushima presents similar challenges, but with the added complication of leaving its imprint on the ocean, a complex system that is vital to human health and the world economy.

Perhaps somewhere a young scientist's career is being shaped by the events unfolding right now in Japan. I certainly hope there is more than one, because the questions we face are many, and they will not be answered soon. Or easily.

The opinions expressed in this commentary are solely those of Ken Buesseler.